Cryogenic apparatus for producing cold



2 Sheets-Sheet 1 July 22, 1969 .1. A. RIETDIJK CRYOGENIC APPARATUS FOR ,PRODUCING COLD Filed June 28, 1967 A w it E w E J. A. RRRRR IJ K C APPARATU FOR PRODUCING LI) 2 Sheets-Sheet 2 United States Patent U.S. Cl. 62-500 5 Claims ABSTRAQT OF THE DISCLOSURE The invention relates to cryogenic apparatus for producing cold, wherein fluid medium flows from a high pressure source through a heat exchanger, then through an ejector where it is expanded and flows to a container. Subsequently medium flows through a throttle means to a second container, with vapor from the second container being returned to the suction inlet of the ejector. A boundary layer of medium adjacent the interior walls of the ejectors diffuser part is drawn off by suction through a recess in the diffuser walls and a duct leading to an area of lower pressure, such as the suction inlet chamber of the ejector.

In known apparatus for producing cold useful for liquefying, a supply of high-pressure medium is cooled in one or more heat exchanges to below the inversion temperature associated with that pressure of the medium. The medium is then throttled in one or more Joule- Kelvin cocks to a considerably lower pressure. With a correctly chosen pressure and temperature in the throttling process, .a temperature decrease of the medium or a phase transition of part of the medium, or both phenomena, will occur in the Joule-Kelvin cocks. The pressure-reduced medium can then be brought in heatexchanging relationship with on object or a medium to be cooled. If a phase transition has taken place, a part of the liquid formed may be conducted away from the apparatus. The low-pressure vapour formed is then conducted away to the atmosphere or returned to .a compressor which supplies the high-pressure medium.

To obtain very low temperatures throttling must be carried out to very low pressure. If, for example, helium is used as the medium and cold is to be produced at a temperature of 42 K., throttling must be carried out to approximately 1 atm.; for 3.6 K. throttling is required to approximately 0.5 .atm. For still lower temperatures throttling must be carried out to even lower pressures. This means that in a closed system the compressor will have to be very bulky while the low-pressure side of the heat exchangers will have to show a low resistance to flow. The result is that these known apparatus are complicated, bulky, and expensive. In addition, the apparatus cannot blow-0E automatically if it is an open system, i.e. the high-pressure medium is dederived from some source or other, while the pressurereduced medium, after heat exchange with the object to be cooled, is conducted away to the atmosphere, and cold has to be supplied at temperatures with which a sub-atmospheric pressure is associated. So measures will have to be taken to conduct away the pressure-reduced medium from the apparatus. A further drawback of the said apparatus is that in the Joule-Kelvin cocks the pressure energy of the high-pressure medium is uselessly dissipated which consequently means a loss.

The invention relates to an apparatus for producing cold and/or for liquefying gases in which the drawbacks of the above described known apparatus are mitigated.

This apparatus comprises at least one supply for medium under high pressure, which supply communicates with one or more heat exchangers in which the high-pressure medium is cooled to below the inversion temperature associated with that pressure. The apparatus comprises at least one ejector to which at least part of the cooled high-pressure medium can be supplied, and the outlet of the ejector communicates, if required through a first container for receiving the pressure-reduced medium. The container has an outlet on one side through which the pressure reduced medium can leave the apparatus via heat exchangers; on the other side of the container is at least one throttle device and, if required, a heat exchanger, through which medium communicates with one or more further containers in which lower pressures prevail, the further containers each communicating with the suction side of the ejector.

Within the scope of the present invention, an ejector is to be understand to mean .an apparatus in which the potential energy of a high-pressure (primary) medium is wholly or partly converted into kinetic energy, the kinetic energy being used, at least partly, for raising the pressure of a second (secondary) medium. In the apparatus to which the invention relates the energy of the high-pressure medium supplied to the ejector is used at least partly for drawing off by suction the vapour from the lower-pressure container and bringing it to the pressure prevailing in the duct system through which the pressure-reduced medium is conducted away from the apparatus. The cold can then be supplied at a pressure which is lower than the outlet pressure. This has the advantage that in an open system the apparatus can blow olf automatically, while the cold is supplied at a pressure lower than the blowing-off pressure. In a closed system where the outlet of a compressor communicates With the supply of high-pressure medium and its inlet communicates with the outlet for pressure-reduced medium, the pressure ratio of the compressor will be considerably lower than is the case in the apparatus in which the high-pressure medium is reduced in pressure in Joule-Kelvin cocks.

In the apparatus to which the invention relates the pressure energy of the medium supplied to the ejector is no longer uselessly dissipated, but is used for pumping up the vapour from the lower-pressure container to the suction pressure of the compressor or to the pressure at which the medium leaves the apparatus again. In this manner an apparatus is obtained having a higher efficiency and a much more favourable pressure ratio in the heat exchanger and the compressor than is the case in apparatus in which Joule-Kelvin cocks are used.

The apparatus to which the present invention relates may be used in particular if cold has to be supplied at very low temperatures. There is now substantial interest in apparatus supplying cold at temperatures which lie below 4 K., in particular for cooling superconductive coils, cryogenic arithmetic and memory elements, for electronic computers and other equipment. As already said, these low temperatures are associated with very low vapour pressures above the liquid bath in the lowerpressure container in which the object to be cooled is placed. If, for example, cold is to be supplied at 1 K., a vapour pressure in the low-pressure container of 0.12 mm. Hg is associated therewith. In order to be able to maintain these low pressures in the further container, a very good operation of the ejector is required.

It is the object of the invention to provide an apparatus of the type described with very simple means and an improved operation of the ejector. The apparatus accord ing to the invention is characterized in that it comprises separating means, which draw off by suction the boundary layer which is formed on the wall of the part of each of the ejectors constructed as a diffuser before that layer would detach from the wall. When medium flows through the diffuser a boundary layer will be formed on the wall thereof. This boundary layer will detach from the wall at a given place in the diffuser, dependent upon a number of factors, and will thus adversely influence the diffuser action. As a result of this, the operation of the ejector also is very adversely influenced. According to the invention, by drawing off by suction that boundary layer before it detaches from the wall, a considerably better ejector operation and a lower attainable suction pressure are obtained.

According to a further favourable embodiment of the apparatus according to the invention, the separating means may be constituted by an annular recess provided in the wall of the diffuser the recess communicating through one or more ducts with a place where a lower pressure prevails than at the area of the recess. The place of lower pressure with which the ducts communicate may be a pump or may be the suction side of one or more further ejectors which will then draw off the boundary layers.

An extremely favourable embodiment of the apparatus in which no additional components need be added to the apparatus is characterized in that each of the ducts communicating with the recess communicates with its other side, with the suction side of the ejector in question. In this case the boundary layer is drawn off by suction of the ejector in question. It has been found, surprisingly, that as a result of this the whole ejector operation is considerably improved.

A further embodiment of the apparatus according to the invention is characterized in that the diameter of the inner wall of the part of the ejector constructed as a diffuser varies stepwise at the area where the boundary layer is drawn off.

In order that the invention may readily be carried into effect it will now be described in greater detail, by way of example, with reference to the accompanying drawings:

FIGURE 1 diagrammatically shows an apparatus including an ejector for producing cold and/ or for liquefying gases;

FIGURES 2 and 3 show, on an enlarged scale, two embodiments of the ejector used in the apparatus shown in FIGURE 1.

Referring now to FIGURE 1, reference numeral 1 denotes a compressor. The compressed medium is first conducted through a cooler 2 in which the heat of compression is dissipated. The compressed medium then flows through a heat exchanger 3 in which it exchanges heat with the lower-pressure medium. The high-pressure medium is then cooled in heat exchanger 4 by means of a cooling device 5 to a temperature of, for example, 60 Kelvin. The high-pressure medium then flows through the heat exchanger 6 in which it again exchanges heat with lower-pressure medium. The high-pressure medium is subsequently cooled in heat exchanger 7 by means of a cooling device 8 to a temperature of, for example, 15 K. after which it again exchanges heat in the heat exchanger 9 with expanded medium. The high-pressure medium then has a temperature which lies below the inversion temperature of that medium at the prevailing pressure.

The medium then enters an ejector 10 in which it is reduced in pressure. The ejector communicates through its outlet 11 to a container 12, and the vapour space of the container 12 communicates, through heat exchangers 9, 6 and 3, to the inlet side of the compressor 1. Condensate from the container 12 can fiow, through heat exchanger 13 and throttle valve 14 in which the liquid is further reduced in pressure, to a container 15 in which a lower pressure prevails than in the container 12.

The vapour space of the container 15 communicates, through heat exchanger 13, with the inlet side 16 of the ejector 10. In the container 15 a cooling spiral 17 is arranged through which a medium to be cooled can flow. Instead of a cooling spiral 17 an object to be cooled, for example, a superconductive coil or a cryogenic arithmetic or memory element of an electronic computer may be arranged in the container 15 which utilizes helium as a medium.

Compressor 1 compresses helium to a pressure P1. This high-pressure medium is cooled in heat exchangers 2, 3, 4, 6, 7 and 9 to below the inversion temperature of this medium at this high pressure, and the high-pressure medium is then supplied to the ejector 10. In this ejector the medium experiences a pressure reduction in which the potential energy is partly converted into kinetic energy, which energy is again used partly for bringing the lowpressure medium at pressure P2 to a higher level pressure.

The medium which leaves the ejector with a pressure P2 is received in the container 12, and the vapor of this medium in the container with a pressure P2 can then flow back again to the compressor through the said exchangers. The liquid formed in the container is in the throttle device 14 to a pressure P3 which is associated with a temperature at which the cold has to be supplied. The vapour in the container 15 of pressure P3 is drawn off by suction of the ejector 10 and brought to heat exchangers 13 and 18 before it enters the ejector 10 where it is raised to a pressure P2 and flowed to container 12. So in this apparatus the compressor operates between the pressures P2 and P1 so that, structurally, this compressor can be much simpler than in apparatus in which throttling takes place in Joule-Kelvin cocks and in which the compressor operates between the pressures P3 and P1.

Further embodiments of this type of apparatus utilizing an ejector as shown in FIG. 1 are described in British patent application 53,418/65 and US. application, Ser. No. 511,044, filed Dec. 2, 1965.

In FIG. 2 the high-pressure medium discharged from the heat exchanger 9 with a temperature of 4 K. for example, is supplied to area 20 of the ejector and to its jet pipe part 21. The ejector further comprises a diffuser part 22 and a suction part 23. The medium which leaves the jet pipe 21 enters the diffuser part 22, and on the wall of said diffuser part a boundary layer of medium is formed and is shown diagrammatically by the vertical shaded area. To prevent this boundary layer from being detached from the diffuser wall at a given point thus adversely influencing the ejector operation, the diffuser wall comprises a recess 24 which communicates with the suction side 23 through ducts 25. In the suction part 23 a lower pressure will prevail than at the area of the recess 24, so that the boundary layer is drawn off to the suction part 23, and thus prevented from being detached from the wall of the diffuser.

In the manner described above an improved ejector is obtained without the use of additional structural components. In an alternative embodiment, instead of making the ducts 25 communicate with the suction part 23, FIG. 2 shows these ducts modified as denoted in broken lines, to communicate with another place where a low pressure prevails, for example, the suction side of a pump or the suction side of a further ejector. FIGURE 3 shows a further embodiment of the ejector in which the recess area of the wall of the diffuser part 22 varies its diameter stepwise, with a resulting step 26, which provides better removal of the boundary layer. Thermal conductivity through the walls of the ejector is prevented by heat-insulating material in the manufacture thereof.

Furthermore, the part 21 of the jet pipe may comprise means for drawing off by suction boundary layers which are formed on the wall of that jet pipe. Also the wall of the part 21 of the jet pipe may be provided with a firing device to enable particles deposited in the solid state on that wall to be volatilized when a small quantity of heat is supplied.

From the above it is clear that with very simple means an improved apparatus for producing cold is obtained in which an ejector is used and in which the medium is reduced in pressure.

What is claimed is:

1. An apparatus for producing cold comprising at least one supply for medium under high pressure, at least one heat exchanger having said supply for medium connected thereto in which said high pressure medium is cooled to below the inversion temperature associated with the selected high pressure, at least one ejector to which at least part of the cooled high pressure medium is supplied, a first container for receiving pressure-reduced medium, the outlet of said ejector communicating through said first container for receiving pressure-reduced medium on the one side through at least one of said heat exchangers with the outlet through which said pressure-reduced medium is adapted to leave the apparatus, at least one throttling device, a second container for said medium in which a lower pressure prevails, means connecting said second container to said first container through said throttling device, means connecting said second container to the suction side of said ejector, and separating means in said apparatus for drawing the medium to contact the entire boundary wall of each of the ejectors constructed as a diffuser before at least a part of said medium detaches from said boundary wall.

2. An apparatus as claimed in claim 1 wherein said separating means are constituted of an annular recess provided in the wall of said diffuser, at least one duct communicating said recess with a location where a lower pressure previals than at the area of said recess.

3. An apparatus as claimed in claim 2 wherein each of said ducts communicates with the recess on one side thereof and on the other side with the suction part of said ejector.

4. An apparatus as claimed in claim 1 wherein the diameter of said inner wall of the part of said ejector constructed as said diffuser is increasingly greater at the place where the separating means is located.

5. A cold producing apparatus comprising a medium supply under high pressure and at a temperature below the inversion temperature associated with said pressure, at least one ejector to which at least part of said high pressure medium can be supplied, at least one heat exchanger through which the outlet of said ejector communicates therewith, and at least one pressure reducing device, said medium being reduced in pressure through said pressure reducing device, and means in said apparatus for drawing said medium to contact the entire boundary wall of said ejector constructed as a difiuser before at least part of said medium detaches from said boundary wall.

References Cited UNITED STATES PATENTS 2,000,741 5/1935 Buckland 23092 2,709,917 6/1955 Bruynes 73--147 2,931,190 4/1960 Dub'itzky 62-191 3,277,660 10/1966 Kemper 6250O 3,360,955 1/1968 Witter 62-514 WILLIAM J. WYE, Primary Examiner US. Cl. X.R. 230-92, 122 

